This invention relates generally to mechanical fasteners and in particular to a tapered pin-key for engaging a part to a shaft.
Pin-keys have long been known and used to engage a part to a shaft or vice versa. Their major use is to prevent relative rotation between a shaft and the rotating members mounted to it. Relative axial motion is also prevented. The part is provided with a bore for receiving the shaft and a keyway intersecting the bore and oriented perpendicular to the axis of the bore. The keyway can either intersect the center of the bore, in which case the shaft would be provided with an aligned diametrical hole, or the keyway can tangentially intersect the bore, in which case the shaft would be provided with an aligned tangential groove in its surface. The pin-key is inserted into the keyway and into the aligned hole or groove in the shaft to engage the shaft and the part.
One of the problems with the prior art pin-key and keyway systems was that exact alignment was required between the keyway and the hole or groove in the shaft. If the keyway and hole or groove in the shaft were made simultaneously by drilling the keyway with the shaft in place, it was difficult to maintain the interchangeability and replaceability of the shafts and parts because of the tendency of a drill to drift into softer material. Since the shaft and part were rarely of the same material, the drill would tend to drift from a vertical line and thus each member and shaft would be slightly different. This problem was especially pronounced in the tangential type keyway. This problem could only be alleviated with special equipment and time consuming and expensive shop procedures. If the part and shaft were to be separately manufactured, precise machining was required to insure that the holes and grooves were properly located. This made the shafts and parts very expensive.
While cylindrical pin-keys and keyways were in general use, the majority of prior art pin-keys and keyways were tapered. The tapered pin-keys and keyways were frustoconical in shape and were preferable over the cylindrical configuration because they achieve a tighter engagement between the part and shaft. The cylindrical pin-key had to be made smaller than the keyway to allow the pin-key to be inserted and removed from the keyway. Thus, there was some play between the shaft and part. In contrast, the tapered pin-key, by virtue of its narrowing configuration, could be inserted into the tapering keyway until it was firmly engaged therein on all sides, thereby eliminating the play between the shaft and part. However, while achieving a tighter engagement than the cylindrical configuration, the tapered pin-keys and keyways had a disadvantage in that they were more expensive to manufacture because their manufacture was difficult, time consuming, and required special equipment. In addition, precise alignment was needed between the keyway and the hole in the shaft.
The pin-key of this invention has a tapered configuration, having two cylindrical surfaces converging at a small angle. The pin-key is designed for use in a keyway tangentially intersecting the bore for receiving the shaft. The tangential keyway is preferable to the keyway extending through the center of the bore, because far less shaft material is removed in making a groove aligned with the tangential keyway than in making a hole aligned with a keyway intersecting the center of the bore. Thus, the shaft is left stronger, with more cross-sectional area to bear torsional or other loads. Furthermore, the surface groove has far less stress concentrating effect than the hole through the shaft.
The tapered configuration of the pin-key of this invention allows the pin-key to achieve the firm engagement of the prior art tapered pins, but because the pin-key is formed from cylindrical surfaces, the pin-key, keyway and groove all have cylindrical rather than tapered surfaces, and are thus easier and less expensive to machine. Furthermore, the precise alignment of the keyway and the groove required for prior art pins is no longer necessary. Variation in the depth of the groove in the shaft is permissible.